Leaking pre chambers will not let air in the fuel system and I doubt if they are the cause of your hard starts. Try to leave the pre chambers in place. Loosen and tighten the collars, repair the injectors. If further tests reveal the pre chambers leaking a little (bubbles in light oil sprayed around collar) it would be good enough for my use.

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Present
1987 300SDL
1991 300SL
1990 560SEL
2001 ML320

Past
1969 200D 1979-82
1983 300SD 1984-85
1972 250C 1982-02
1995 S350 2011
1997 S320 2012